   [n]
   (first (drop (dec n) (filter prime? (drop 2 (range))))))
 
+(def problem-8-number 7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450N)
+
+(defn problem-8
+  "Return the greatest product of 5 consecutive digits in a number."
+  [n]
+  (let [p       (map #(java.lang.Integer/parseInt %) (rest(string/split (str problem-8-number) #"")))
+        result  (atom 0)]
+    (loop [sequence p]
+      (let [digits (take 5 sequence)]
+        (if (not-any? zero? digits)
+          (let [product (apply * digits)]
+            (if (> product @result)
+              (reset! result product))))
+        (if (< (count sequence) 6)
+          @result
+          (recur (rest sequence)))))))
+
 (defn -main
   [& args]
   (time (println "Problem 1: " (problem-1-smart 1000)))

  (time (println "Problem 4: " (problem-4)))
  (time (println "Problem 5: " (problem-5 1 20)))
  (time (println "Problem 6: " (problem-6-smart 100)))
  (time (println "Problem 7: " (problem-7 10001))))

(defn squared-natural-numbers
  "Return a lazy sequence of the natural numbers squared."
  []
  (map #(* % %) (rest(range))))

(defn problem-6
  "Return the difference between the sum of the squares of the first n natural numbers, and the square of the sum."
  [n]
  (let [sum-of-squares (apply + (take n (squared-natural-numbers)))
        sum            (apply + (take n (rest(range))))
        square-of-sum  (* sum sum)]
    (math/abs (- square-of-sum sum-of-squares))))

